Stripping still-dephlegmator operation



April 26, 1960 E. s. PALMER, JR

STRIPPING STILL -DEFHLEGMATOR OPERATION Filed Oct. 28, 1957 INVENTOR,f1.5. PALMER,JR.

linited States ff 2,934,491 STRIPPING STILL-DEPHLEGMATOR orERArroNEverett S. Palmer, Jr., Bartlesville, Okla., assignor t PhillipsPetroleum Company, a corporation of Delaware Application October 28,1957, Serial No. 692,645

11 Claims. (Cl. 208-104) 'This invention relates to absorber-strippingstill- -dephlegmator operation. In one aspect it relates to a lowpressure still-dephlegmator operation. In another v.aspect it relates tomeans and a method for improving .the eiciency of a pump, particularly ajet pump, for '20 ,pumping hot dephlegmator oil to a low pressure'still.'

, In the operation of jet pumping low pressure hot vfdephlegmatorf oilfrom the bottom of a dephlegmator to the top' of'a lowipressure still byusing drive oil from a lhigh pressure still in atwo-still distillationloperation, it has been noted that the gasoline and water content in thedephlegmator oil alects the jet pump efficiency. The pressure reductionin the jet suction results in vaporiza- .tion ofvolatile material inprocess andv inashing of vvater since the volatile material and watermixture is at Aa boiling point'consistent with the pressure in thebottom tof the dephlegmator. This vaporizing and flashing in the.suction of the jet pump is further aggregated by the small pressuredrop of the de'phlegmator oil owing through valved piping to thepumpsuction. There isa pressure ydrop even if this valved piping is short.In an operation employing a two-still system for recovering absorbedKgasoline boiling range hydrocarbons from a rich absorp- :tionV oil thevolatile material in process is the gasoline lb'oilingrange-hydrocarbons. Thus, in this cas-e the flashed water and gasolinevapor reduce the capacity of the jet pump and this reduction in capacityover normal capacity, if no ashing occurred, approaches around A25percent. 'In other words the actual capacity of the pump with theAliashing is about 75 percent of the capacity if no flashing occurred.`

To eliminate, or at least substantially minimize, this yiiashing inthesuction of a jet pump, I provide a flash pot or `a flash separatorvessel in the suction line between the dephlegmator and the pump. Inthis flash vessel easily vapor'iied materials are flashed and removedfrom the liquid, and `with removal of the most volatile constituents ofthe dephlegmator oil considerably less'flashing in the suction of thejet pump occurs. Furthermore, I provide Aa pipe for'returning the ashedvapors to the dephlegmator so that the flashed materials will not belost to the operation. I also provide in the Hash vessel means forremoval of entrained water so as to reduce the content of water in theoil reaching' the jet pump.

An object of my invention is to provide apparatus and gav methodfor'operationof a rich absorption oil stripping Vanddephlegmator system.y i

Another object of my invention is to provide an eiicient apparatus andmethod for returning'dephlegmator oil to the top of a low pressurestill.

Still another object of my invention is to provide means and a methodfor increasing the eiciency of a jet pump utilizing'` available plantpressure for returning dephleg- `mator oil totheltopof a lowpressures'till.

2,934,49l Patented Apr. 26, 19,60

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or from a lower portion of a dephlegmation zone at alevel higher thansaid low leveland separating the withdrawn oil into a phase separationzone and therein separating a vapor phase from liquid oil, withdrawingseparated liquid oil from said phase separation zone and transferringthis Withdrawn oil. by jet action into the upper portion of a lowpressure distillation zone. A high pressure still bottoms, which isnormally fed to the low pressure still, is used as drive oil in the jetpump. Y

My invention further includes a distillation-dephlegmater system, incombination, a dephlegmator, a low pressure still, a high pressurestill, a vapor-liquid separator, a first conduit communicating thenormally liquid oil-containing portion of said dephlegmator Vwith saidvapor-liquid separator, a second conduit communicating the normallyvapor-containing space of said separator with the upper portion of saiddephlegmator, a third conduit communicating the lower portion of saidhigh pressurestill with the upper portion of said .low pressure still, ajet pump in said third conduit, a fourth conduit communicating thenormally liquid containing space of said vapor-liquid separator with thesuction inlet of said 'et pump, a fifth conduit communicating the upperportion of said low pressure still with the upper portion of saiddephlegrnator at a level below the level of commu- Y nication of saidsecond conduit with the upper portion of said dephlegrnator, means forinlet of cooling water to and outlet of used cooling water from saiddephlegmator, separate inlets for stripping steam to said stills andinlet for oil to be distilled to said high pressure still and outletsfor olf gases from said high pressure still and from said dephlegmator.

i will describe, as an example of the apparatus and process of myinvention, the apparatus and process of an absorption-distillationoperation for extracting normally liquid gasoline boiling rangehydrocarbons from natural gases. in the drawing reference numeral 1identitles an absorber column. A wet gas inlet 2, a dry gas outlet 3, alean absorption oil inlet 6 and a rich absorption oil outlet 5 areprovided with this absorber, as understood by those skilled in the art.This absorber column or vessel is provided with conventionalvapor-liquid contacting apparatus 4, such as bubble cap trays. A highpressure still 8 is provided with a rich oil inlet 5, a stripped gasoutlet vapor-liquid contacting apparatus il, and a bottoms oil removaloutlet 10. A pipe 19 is provided for inlet of stripping steam to thisstill. A low pressure still lo is provided with a conduit 12 for inletof liquid to be distilled, a vapor outlet line 18, a lean oil outletline 6, and a second line 15 for inlet of liquid to be distilled. Steamfor operation of still is introduced through a pipe 20. This lowpressure still is also proassaggi further cooling of the hot lean oilwith an extraneous cooling agent if needed. Additional heat foroperation of still 8 is provided from the steam entering through pipe19. Pipe 10 branches into pipe 12 and pipe 13. Pipe 13 is provided witha motor valve 37 and terminates in the power liquid inlet or driveliquid inlet of a jet pump 14. A pipe 36 communicates a flash separatortank 31 with the inlet to jet pump 14. A pipe 15 is provided for passageof liquid from jet pump 14 to the upper portion of low pressure still16.

The vapor-liquid separator 31 is provided with a baille plate 33, asillustrated. A pipe 32 communicates the normally vapor containing spaceof separator 31 with the upper portion of a dephlegmator vessel 21. Apipe 30 is provided for withdrawal of water from the lower portion ofthe separator 31.

The dephlegmator vessel 2l is provided in its upper portion withconventional vapor-liquid contacting apparatus 23 which can, if desired,be bubble cap trays or other suitable vapor-liquid contacting apparatus.A pipe 22 is provided at the top of the dephlegmator for removal of offgases. At an elevation well down the column 21 is a do-nut tray 26. Thisdo-nut tray is provided for removal of water from the upper portion ofthe dephlegmator while allowing oil to ow through an opening in thecenter of the tray to the lower portion or normally kettle portion ofthe column 21. Such liquid take-off trays as do-nut tray 26 are wellunderstood by those skilled in the fractionation art. A pipe 2S isprovided for removal of water from this tray. A pipe 29 is provided forpassage of oil, commonly called dephlegmator oil, from the lower portionof dephlegmator 21 to the vaporliquid separator 31. A pipe 45 is forremoval of Water from the bottom part of the dephlegmator. A pipe 24 isprovided for inlet of cooling water to the upper portion of dephlegmator21.

In thel operation of this apparatus a wet natural gas, that is, onecontaining eXtractable or condensable gasoline boiling rangehydrocarbons, is introduced into absorber 1 through a pipe 2, the drygases (free or substantially free from said condensable hydrocarbons)being removed therefrom through pipe 3. Lean absorption oil enters thecolumn through pipe 6 and flows downward over packing apparatus 4 and isremoved as a rich oil through pipe 5. The outlet of this rich oil isregulated by a oat control apparatus 39. After passing through heatexchanger 7 for heating the rich oil, the heated rich oil is introducedinto the upper portion of the high pressure still 8. This rich oil thenflows downward over the vapor-liquid contact promoting apparatus 11 incountercurrent contact with steam introduced through pipe 19. Thestripped gases leave this still through pipe 9. The partially denudedabsorption oil leaves the high pressure still through pipe 10 and in oneoperation this partly denuded oil from the high pressure still, atsubstantially the pressure maintained in the still, is divided into twoportions. One portion passes through pipe 12 directly into the upperpart of the low pressure still for removal of the remainder of theabsorbed hydrocarbons. The other portion ows on through pipe 13 andthrough the jet pump 14 and pipe 15 into still 16. This high pressureoil, on passing through jet pump 14, draws dephlegmator oil from thevapor-liquid separator 3'1 and transfers this withdrawn oil, along withthis portion of the high pressure oil, through pipe 15 into the upperportion of the low pressure still 16.

A liquid level control assembly 39 and similar assemblies 40 and 41 areprovided for regulating the removal of liquid bottoms from absorber 1,still S and still 16, respectively. A similar liquid level controllerassembly 42 is provided in conjunction with vapor-liquid separator 31for withdrawal of a water phase 35. A liquid level control assembly 44is provided for withdrawal of water 28 from the bottom of thedephlegmator vessel.

A liquid level control apparatus 43, which includes a float apparatus38, and a motor valve 37, is intended to regulate the rate of flow ofdrive oil from the high pressure still 8 in response to the level of thedephlegmator oil 27 in the dephlegmator 21. I-n this patricularoperation the control assembly 43 is so arranged as to increase the rateof ow of drive oil through valve 37 upon an increase inthe level of thedephlegmator oil above a predetermined level and to throttle valve 37 incase the level of the dephlegmator oil falls below the predeterminedlevel. A valve 46 in pipe 29 is normally open and, of course, a checkvalve 47 in this line allows ow of dephlegmator oil only from thedephlegmator to the ash tank 31. Thus there is a free flow ofdephlegmator oil from the dephlegmator to the ash vessel. Accordingly,when the jet is not transferring the dephlegmator oil sufcientlyrapidly, the level of the dephlegmator oil in the dephlegmator risesand, under this condition, the float control apparatus 38 actuates themotor valve 37 to open same and allow the passage of more drive oil, andthe greater the volume of drive oil owing through jet 14 the moredephlegmator oil is removed from the dephlegmator through the flash tank31. Under this condition, then, the level of the dephlegmator oil in thedephlegmator will fall and when it falls to a level below thepredetermined normal operating level, the oat apparatus 38 actuatesvalve 37 to throttle same and. reduce the ilow of drive oil through thepump 14. In this manner the rate of pumping of the dephlegmator oil isregulated. Provision is made in the ash tank 31 for a phase separationto take place between the entrained water and dephlegmator oil.Reference numeral 35 identities water settlings in this separator vesseland reference numeral 34 identifies the larger volume of dephlegmatoroil in this tank.

In one instance a high pressure absorber operating on a wet natural-gasis operated at a pressure of from 250 to 1,000 p.s.i.g. (pounds persquare inch gauge). The lean absorption oil owing downward through thisabsorber is a conventional mineral seal oil and is maintained at atemperature as near atmospheric temperature as possible. The highpressure still is operated at a pressure ordinarily between about 235and 250 p.s.i.g. The low pressure still isoper'ated between pressures ofabout 45 and 60 p.s.i.g. -The top still temperature of the low pressurestill is, in this case, between the limits of about 380 and 400 F., thatalso being about the temperature of the bottoms oil from the highpressure still as it enters the upper portion of the low pressure still.On account of pressure loss of materials in process through piping, thepressure ordinarily maintained in the dephlegmator is about 3 to 5pounds less than the pressure maintained in the low pressure still. Forexample, if the pressure in the low pressure still is maintained at 60p.s.i.g., then the pressure in the dephlegmator is about from 55 to 57p.s.i.g. The temperature of the water entering the top of thedephlegmator through pipe 24 is that which can be obtained from thecooling towers of the plant. The temperature of the gases leaving thetop of the dephlegmator and the temperature in the top of thedephlegmator are within the limits of about to 215 F. The temperature ofthe dephlegmator oil in the lower portion of this dephlegmator rangesfrom about 270 to about 283 F.

Throughout this specilication and claims the term upper portion of thedephlegmator is intended to mean the portion of the dephlegmator abovethe do-nut tray 26. This portion, that is, the portion above do-nut tray26, includes the vapor-liquid contact promoting apparatus 23. The termlower portion ofthe dephlegmator is intended to mean the portion of thedephlegmator below the donut tray 26 and this lower portion includes theportion normally corresponding to the kettle of a still. This lowerportion includes the space in which liquid water 28 and the dephlegmatoroil 27 separate..

By removing vapors or ash vapors from dephlegmator oil according to myinvention the pumping rate of the will aesinet-1 dephlegmator 5 oil islincreased between the limits of about Sto 4` 10v percent overthe-pumping rateY when the-vaporliquidseparator 31--is -not employed. Itis realized that the mechanical construction of pipe 29 and pipe 36,without theuse of the vapor-liquid separatorl, has a con` siderableeffect onthe rateofpumping ofthe jet pump. That is, without theuse ofthevapor-liquid separator the size of the pipe, its length, and the numberand type-of valves disposed in this pipe leading from the dephlegmatorto the suction of the pump have a considerable eiect on the rate ofpumping of the dephlegmator oil. With properly designed pipes leadingfrom the dephlegmator to the separator and thence to the suction of thejet pump 14, and with the instalaltion of my vapor-liquid separator, thepumping rate of the pump is increased about, for example, 3 to 10percent. With properly designed pipes (sullciently large and with aminimum of valving) for transfer of dephlegmator oil from thedephlegmator to the suction of the jet pump, upon installation of thevapor-liquid separator, the pumping capacity of the pump may beincreased as much as percent. While an increase in pumping rate of from3 to 10 percent may, at rst sight, not appear to be very advantageous,yet when large volumes of liquid are transferred by such a pump, anincrease in pumping rate of from 3 to l0 percent is a material increasein pumping rate.

While certain embodiments of the invention have been described forillustrative purposes, the invention obviously is not limited thereto.

I claim:

1. A process comprising withdrawing hot dephlegmator oil containingentrained water and other vaporizable material and at its boiling pointfrom a lower portion of a dephlegmation zone, introducing this withdrawnhot oil into a phase separation zone and therein separating a vaporphase from a liquid oil phase, passing the separated vapo-r phase intothe upper portion of said dephlegmation zone, withdrawing separatedliquid oil from said phase separation zone and transferring thiswithdrawn liquid by jet action into the upper portion of a low pressuredistillation zone.

2. A process for transferring hot dephlegmator oil from the lowerportion of a dephlegmation zone into the upper portion of a low pressuredistillation zone, cornprising withdrawing hot dephlegmator oilcontaining entrained water and other vaporizable material and at itsboiling point from the lower portion of said dephlegmation zone andpassing same into a phase separation zone, separating a vapor phase froma hot liquid oil phase in this latter zone, venting the separated vaporfrom said phase separation zone into the upper portion of saiddephlegmation zone, withdrawing hot bottoms oil from a high pressuredistillation zone, passing this withdrawn hot bottoms oil through ajetting zone as drive oil, drawing the separated hot liquid oil phaseinto said jetting zone by the jetting action of said drive oil, andpassing the drive oil and hot liquid oil phase into the upper portion ofsaid low pressure distillation zone.

3. In the process of claim 2, regulating the rate of passage of saidhigh pressure hot bottoms liquid through said jetting zone in responseto the liquid level of said hot dephlegmator oil in the lower portion ofsaid dephlegmation zone.

4. A distillation-dephlegmation operation comprising, withdrawing hotdephlegmator oil containing entrained water and other vaporizablematerial and at its boiling point from the lower portion of adephlegmation zone and passing same into a phase separation zone,separating a vapor phase from a hot liquid oil phase in this latterzone, venting the separated vapor phase from said phase separation zoneinto the upper portion of said dephlegmation zone, withdrawing hotbottoms oil from a high pressure distillation zone, passing thiswithdrawn hot bottoms oil through a jetting zone as drive oil, drawingthe separated hot liquid oil phase into said jetting zone by the jetting-a'ctioriotsaidA `drive oil, passir'lgthdriv `oil and hotfliquid oilphase intdthe upper portion Iof l`alow pressure distillation zone,introducing rich absorption oil feed and stripping steam into the upperand lower portions, respectively, ofs'aidfhigh pressure distillationzone, introducing stripping steam into the-lower portion of said lowpressure distillation zone, maintaining s'aid high pressureA andsaid lowpressure'distillationzones under respectively high pressure and lowpressure distillation conditions, removing oif-gases from said highpressure and from said low pressure distillation zones, passing theott-gases from said low pressure distillation zone into the upperportion of said dephlegmation zone at a level below the level of entryof said separated vapor phase, maintaining said dephlegmationl zoneunder dephlegmation conditions by introducing cooling water into theupper portion of said dephlegmation zone and therein directly contactingthis introduced water with said vapor vented thereinto and with saidoff-gases from said low pressure distillation zone, and withdrawing usedcooling water therefrom, withdrawing off-gases from the upper portion ofsaid dephlegmation zone, and removing distilled oil bottoms from saidlow pressure distillation zone.

5. In the operation of claim 4, dividing the withdrawn hot bottoms oilfrom said high pressure distillation zone into two portions, passing oneportion into said jetting zone as said drive oil and introducing theother portion directly into the upper portion of said low pressuredistillation zone.

6. In the operation of claim 5, regulating the rate of ilow of said oneportion of said withdrawn hot bottoms oil into said jetting zone as saiddrive oil in response to the level of said dephlegmator oil in the lowerportion of said dephlegmation zone.

7. In the operation of claim 4, maintaining said high pressuredistillation zone under a pressure within about 235 to 250 p.s.i.g., thelow pressure distillation zone within about 45 to 60 p.s.i.g., and thedephlegmation zone at a pressure from 3 to 5 p.s.i.g. less than thepressure maintained in said low pressure distillation zone.

8. In the operation of claim 4, maintaining the temperature of thedephlegmator oil in said dephlegmation zone within about 270 to 283 F.

9. A distillation-dephlegmator system comprising, in combination, adephlegmator, vapor-liquid direct contact promoting means disposedoperatively in said dephlegmator, a low pressure still, a high pressurestill, a vaporliquid separator, a rst conduit communicating the lowerportion of said dephlegmator with said vapor-liquid separator, a secondconduit communicating the upper portion of said separator with the upperportion of said dephlegmator, a third conduit communicating the lowerportion of said high pressure still with the upper portion of said lowpressure still, a jet pump in said third conduit, a fourth conduitcommunicating the lower portion of said vapor-liquid separator with thesuction inlet of said jet pump, a fifth conduit communicating the upperportion of said low pressure still with the upper portion of saiddephlegmator at a level below the level of communication of said secondconduit with the upper portion of said dephlegmator, means for inlet ofcooling water to and outlet of used cooling water from saiddephlegmator, separate inlets for stripping steam to said stills, aninlet foroil to be distilled to said high pressure still, an outlet forbottoms liquid from said low pressure still, and outlets for off gasesfrom said high pressure still and from said dephlegmator.

10. In the apparatus of claim 9, a sixth conduit communicating saidthird conduit intermediate said high pressure still and said jet pumpwith the upper portion of said low pressure still.

11. ln the apparatus of claim 10, a motor valve in` said third conduitintermediate said jet pump. and the point of communication of said sixthconduit with said third conduit, and a liquid level control means forregu-- lating liquid flow through said motor valve in response to levelof liquid oil in the lower portion of said dephlegmator.

References Cited in the le Yof this patent .UNITED STATES PATENTSWorkman Nov. 27, 1934 y Y OTHER REFERENCES L Perry: Chemical EngineersHandbook (1950), 3rd Ed.,

McGraw-Hill Book Co.,New York,v New York,vpage ming. 4N

1. A PROCESS COMPRISING WITHDRAWING HOT DEPHLEGMATOR OIL CONTAINING ENTRAINED WATER AND OTHER VAPORIZABLE MATERIAL AND AT ITS BOILING POINT FROM A LOWER PORTION OF A DEPHLEGMATION ZONE, INTRODUCING THIS WITHDRAWN HOT OIL INTO A PHASE SEPARATION ZONE AND THEREIN SEPARATING A VAPRO PHASE FROM A LIQUID OIL PHASE, PASSING THE SEPARATED VAPOR PHASE INTO THE UPPER PORTION OF SAID DEPHIEGMATION ZONE, WITHDRAWING SEPARATED LIQUID OIL FROM SAID LIQUID BY JET ACTION INTO THE UPPER PORTION OF A LOW PRESSURE DISTILLATION ZONE. 